"The shark to me looked almost like a stamp. The lighting on the people was different to the lighting on the shark and the shark was not deep enough for the lighting to vary that much," Moir said.

"But the real difference was the shadows on the shark. There should have been a fading of the shark from its nose, which was closest to [the camera] to its tail, which was furthest from [the camera], because of the water clarity.

"It should have been darker and easier to see the shark at the nose than the tail but it's uniform," he said.

"That's why I became a bit suspicious," he said.

"I'm not going to say 100 per cent it's not real. But generally if you want to prove an image is real then hand over the original files," he said.

Instagram user @QuothRaven appeared to provide further support for the hoax theory when he found an old photograph of a shark that he says matched Mr Anderson's hazy image.

A great white shark swimming off the coast of Mexico was snapped by National Geographic in 2014 and appears to bear the same outline as the shark in the alleged Bondi sighting.

Bondi lifeguards also question the veracity of Mr Anderson's claim.

"The lifeguards said that it may have been photoshopped, to their understanding," a spokeswoman for Waverley Council said in a statement to Fairfax Media.

"Council can't verify that photograph. We haven't had a sighting for weeks and believe it may be a hoax.

"As far as whatever that photo is portraying, there have been no shark sightings for two to three weeks," the statement said.

Fairfax Media repeatedly tried to contact Mr Anderson on Thursday afternoon, but he could not be reached on the number used to contact him earlier this week.

On Tuesday, Mr Anderson said he and his squad had gone out for a swim off Bondi about two weeks ago when they decided to check out the shark nets, which stretch across the bay.

"There has been a lot of shark mania at the moment, so I wanted to take my swimmers out to the shark nets to show that they are real and they are there and they stop sharks coming in," he said.

Mr Anderson said that, when they reached the nets, the group dived down between five and 10 metres and, as he was returning to the surface, he snapped a few photographs on his GoPro camera, which he usually takes on his fitness outings.

No one in the group was aware of their close encounter with the shark until the photograph emerged, Mr Anderson said.

"I was coming back up and you can actually see, I was aiming back up towards the sun, and the shark was on my left and I didn't see it until I downloaded the photos," he said.

Mr Anderson said he posted the photograph on Instagram after carefully considering what the reaction would be. He said his experienced swimmers were "pretty cool" about the incident.

"I've got two distinct groups: the experienced, hard-core ocean swimmers and the rookie swimmers. My experienced group don't seem to care that much ... because they're kind of accepting," he said.

"I think there is a little bit of a placebo living in the Sydney area, with people behind shark nets. They've got a false sense of security."

Mr Anderson, who spends a lot of his time in the water, said that, since the photograph was taken, he had seen another shark while he was stand-up paddle boarding off Clovelly.

"For me personally, it's like 'Wow, this is close,' but I've actually seen a lot of sharks. I'm a little bit more neutral about it.